1. Field of the Invention
This invention relates to a light-emitting substance and a manufacturing method thereof. More particularly, it relates to a method for manufacturing a so-called nanocrystal light-emitting substance.
2. Description of the Related Art
Recently, the nano crystal structure in II-VI group semiconductors, such as ultra-fine particles or porous silicon, typified by Si or Ge, is stirring up notice in that the crystal exhibits peculiar optical properties. The nano crystal structure means crystal grains having the crystal size of the order of a few nanometers and is usually known as nanocrystals.
If, in the II-VI group semiconductors, the above-mentioned nano structure crystal and the bulk structure crystal are compared to each other, the former exhibits more desirable light absorbing and emitting characteristics. This is presumably ascribable to the fact that the II-VI group semiconductors having the nano structure crystal has a band gap larger than that in the bulk crystal structure because of the quantum size effect. That is, in the II-VI group semiconductors having the nano structure crystal, the band gap is retained to be increased due to the quantum size effect.
Meanwhile, a variety of light emitting substances are used in a display, such as a television display. The light emitting substance, currently used in a display, such as television display, is synthesized by firing the starting material at an elevated temperature. The synthesized light emitting substance has a particle size of the order of micrometers (3 to 10 xcexcm).
On the other hand, there is recently raised a demand for a thin type display in the field of e.g., television. Thus, a plasma display as a lightweight flat display, termed herein a PDP, a field emission display, termed herein a FED, or an electroluminescence display, termed herein an ELD, is stirring up notice.
Of these, the FED is attracting utmost notice. With the FED, the electron beam voltage is much lower than that of e.g., the CRT. Thus, if the conventional light emitting substance, having the grain size of the order of a few um, there is raised a problem that sufficient light emission cannot be achieved because of the extremely low voltage of the electron beam. The reason is possibly that the irradiated electron beam cannot reach the light-emitting site of the light emitting substance because of the large-sized structural crystals of the conventional light emitting substance.
It may, therefore, be said that a light emitting substance that can be excited at a lower voltage is suited for the thin type display, in particular the FED. The II-VI group semiconductors, having the above-described nano structure crystal, may be recited as the light emitting substance satisfying this requirement.
On the other hand, zinc oxide, represented herein as ZnO:Zn, emitting green to blue light, may be recited as being a light emitting substance emitting the light at a lower voltage. Specifically, this ZnO:Zn is used in the FED and can be excited at a voltage as low as hundreds to thousands volts. This ZnO:Zn has a crystal structure of a micro size and exhibits electrically conductivity such that it can emit light without charge-up even at a lower voltage.
With a light emitting substance having the nano structure crystal, even the electron beam radiated at a lower voltage can reach the light emitting site of the light emitting substance. Thus, the light emitting substance having the nano structure crystal can be used with advantage for the above-described thin-type display.
However, at present, there is no practically utilized light emitting substance that can be excited at a low voltage, with the exception of the above-mentioned ZnO:Zn. The manufacturing method for the II-VI group semiconductors, having the nano structure crystal, has not been sufficiently investigated, such that no desirable light emitting substance can be manufactured. Thus, a manufacturing method for a light emitting substance usable advantage for the type display has been a desideratum.
There is also raised a demand for a fine light emitting substance for ultra-high definition CRT or a light emitting substance of high light emitting efficiency emitting the light by ultraviolet light for ELD. Thus, a new method for manufacturing this light emitting substance has also been a desideratum.
It is therefore an object of the present invention to provide a novel manufacturing method for a light emitting substance of high light emitting efficiency having the nano structure crystal and which is satisfactorily doped with an activator.
In one aspect, the present invention provides a light emission substance formed of a nanocrystal light emission substance, with a mean crystal size of 2 to 5 nm, activated by an activator and irradiated with ultraviolet light.
In another aspect, the present invention provides a method for producing a light emission substance including illuminating the ultraviolet light on a nanocrystal light emission substance of a mean crystal grain size of 2 to 5 nm activated with an activator.
In yet another aspect, the present invention provides a method for manufacturing a color cathode ray tube having at least a portion of a phosphor surface thereof formed by a light emission substance formed of a nanocrystal light emission substance of a mean crystal size of 2 to 5 nm, activated by an activator and irradiated with ultraviolet light.
With the manufacturing method for the light emission substance according to the present invention, there may be produced an ultra-fine nanocrystal light emission substance that is able to be excited to emit light even at a low voltage and that has an extremely high light emitting efficiency.
The nanocrystal light emission substance, prepared by this method, can be applied with advantage to FEDs, high definition CRT or ELD.